An ink jet recording apparatus has been known, which has a recording head for discharging ink as droplets onto a recording medium to print an image. The ink jet recording apparatus is provided with at least an ink container containing ink, to supply the ink from the ink container to the recording head. In a serial ink jet recording apparatus, a recording head is mounted to a carriage that moves back and forth in a main scanning direction, a widthwise direction of a recording paper. Each time the carriage makes one lap, the recording head records a line of image, and then the recording paper is fed in a sub scanning direction orthogonal to the main scanning direction by an amount corresponding to the image line. Thus, an image frame is printed serially line after line.
Because the ink is a consumable material, the ink container is often formed as a cartridge that is removably attached to the ink jet recording apparatus, so as to make it easy to refill the ink. Such a cartridge type ink container, hereinafter called the ink cartridge, is attached to the carriage carrying the recording head, mostly above the recording head.
In an ink jet recording apparatus where an ink cartridge is disposed above a recording head, an ink load in the ink cartridge becomes positive to inner pressure of the recording head, which causes a concern that the ink could leak out of the nozzle of the recording head. Therefore, in order to keep the pressure in the recording head negative, a negative pressure generation member is disposed in the ink cartridge. The negative pressure generation member is a porous material, including for example a sponge. Due to its capillary force, the negative pressure generation member absorbs and holds the ink in the ink cartridge. Thereby, the inner pressure of the recording head, which is interconnected through an ink supply path to the ink cartridge, is kept negative. Forming meniscuses in the nozzles of the recording head prevents the ink from leaking out of the nozzles.
Japanese Laid-open Patent Application No. 2002-200774 discloses a method of filling such a cartridge with ink. As shown in FIG. 12A, an ink cartridge 121 in the patent document contains a negative pressure generation member 123 in a case 122 which stores ink, and an ink outlet 124 for supplying the ink to a recording head is disposed on a bottom of the case 122. As the ink decreases with the supply of the ink, air is led through an air inlet 126 into the case 122. In the air inlet 126, a gas-liquid separation filter is provided, which does not let liquid pass through it, but only gas.
Since a not-shown filter or valve is placed in the ink outlet 124, flow resistance through the ink outlet 124 is large. Therefore, besides the ink outlet 124, the ink cartridge 121 has an ink filling opening 128 formed through a side wall of the case 122. For the ink filling, an ink supply tank 130 is connected to the ink filling opening 128, and a sucking pump sucks the air from the case 122 through the air inlet 126, to decompress the air inside the case 122. Thereby, the ink moves from the ink supply tank 130 into the case 122.
The ink filling opening 128 is arranged such that a distance L1 from the ink supply outlet 128 to the ink outlet 124 is shorter than a distance L2 to the air inlet 126. Thereby, the ink entering through the ink filling opening 128 reaches the ink outlet 124 faster than the air inlet 126 and the ink go around the ink outlet 124. This configuration is for preventing formation of air pools around the ink outlet 124, the air pool being a room in which only air exists but no ink exists. The air pools around the ink outlet 124 result in forming air bubbles in the nozzles, which chokes the nozzles and causes defective discharge.
As shown in FIG. 12B, however, if there is ink residue 132 around the ink outlet 124 and an air pool 133 is formed in the ink outlet 124 when the ink cartridge 121 is refilled with ink, flow resistance against the ink is larger in the area where the air pool 133 exits than the area where the ink residue 132 exits. Therefore, there are concerns that the ink taken from the ink supply tank 130 may not flow into the air pool 133, so the air pool 133 may stay after the refill of the ink.